The present invention relates to a surgical screw system for use with implantation rods, and related methods of using a surgical screw system with implantation rods.
The bones and connective tissue of an adult human spinal column consists of more than 20 discrete bones coupled sequentially to one another by a tri-joint complex. The complex consists of an anterior disc and two posterior facet joints. The anterior discs of adjacent bones are cushioned by cartilage spacers referred to as intervertebral discs. The over 20 bones of the spinal column are anatomically categorized as one of four classification: cervical, thoracic, lumbar, or sacral. The cervical portion of the spine which comprises the top of the spine up to the base of the skull, includes the first 7 vertebrae. The intermediate 12 bones are thoracic vertebrae, and connect to the lower spine comprising the 5 lumbar vertebrae. The base of the spine is a sacral bones (including the coccyx).
The spinal column of bones is high complex in that it includes the over 20 bones coupled to one another, housing and protecting critical elements of the nervous system having innumerable peripheral nerves and circulatory bodies in close proximity. Despite its complexity, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction.
Genetic or developmental irregularities, trauma, chronic stress, tumors and disease, however, can result in spinal pathologies which either limit this range of motion, or which threatens the critical elements of the nervous system housed within the spinal column. A variety of systems have been disclosed in the art which achieve this immobilization by implanting artificial assemblies in or on the spinal column. These assemblies may be classified as anterior posterior or lateral implants. Lateral and anterior assemblies are coupled to the anterior portion of the spine which is in the sequence of vertebral bodies. Posterior implants generally comprise pairs of rods, which are aligned along the axis which the bones are to be disposed, and which are then attached to the spinal column by either hooks which couple to the lamina or attach to the transverse processes, or by screws which are inserted through the pedicles.
It is desirable, during surgical implantation of such orthopedic devices, to have a multi-axial screw system that provides a consistent lock as well as reliability, durability, and ease of installment.
The present invention relates to a surgical screw system for use with implantation rods. In one embodiment, the system comprises a screw member, a receiver member, a pressure cap and a locking device. The screw member has a head and shaft; the head of the screw member has a spherical undersurface and a conical tapered recess. The receiver member has upper and lower portions, a u-shaped receiving channel and an axial bore. The u-shaped channel has two lateral legs at the upper portion of the receiver member and forms an opening leading to the axial bore; the conical surface has a diameter larger than the shaft of the screw member and a diameter smaller than the head of the screw member. The conical surface forms a support upon which the spherical undersurface of the head of the screw member rests when the screw member is guided through the bore to the lower portion of the receiver member. The pressure cap of the system is positioned within the axial bore of the receiver member and is situated upon the head of the screw member; the pressure cap has upper and lower portions and the upper portion of the cap comprises a concave radial portion upon which the rod is positioned, and the lower portion comprises a spherical portion positioned upon the conical tapered recess of the head of the screw member. The locking device is designed for securing the rod within the u-shaped channel of the receiver member by applying a tightening torque upon the rod when positioned within the opening and the bore near the upper portion of the receiver member.
In another embodiment, the undersurface of the head and the shaft of the screw member comprise threaded portions. In still another embodiment, the legs of the u-shaped channel has internal threads and the threads may be buttress threads.
In a further embodiment, the conical tapered recess of the head of the screw member comprises an aperture coaxial to the shaft and designed to engage a fastening device. The pressure cap further comprises an axial bore extending from the upper through lower ends of the cap; the bore of the pressure cap corresponds to the aperture of the head of the screw member allowing an access for the fastening device.
In still a further embodiment, the receiver member further comprises a rectangular key-locking segment and a cylindrical undercut situated adjacent to the bore. In yet a further embodiment, the pressure cap further comprises a cylindrical undercut and a retaining ring; the key-locking segment and the undercut of the receiver member are designed to engage the undercut and the ring of the pressure cap to form an anti-rotation and locking mechanism.
In yet another embodiment, the legs of the u-shaped channel of the receiver member further comprises a threaded portion and the locking device further comprises a corresponding threaded portion. In another embodiment, the threaded portions are buttress threads. In yet another embodiment, the locking device is a set screw. In still another embodiment, the locking device is a top locking nut. In still yet another embodiment, the aperture of the head of the screw member is hexagon-shaped and the fastening device is a hexagon socket screw key.
In another embodiment, the axial bore of the receiver member comprises a plurality of slots descending down the legs of the u-shaped channel and the locking device comprises at least one protrusion designed to engage at least one of the slots on the legs of the u-shaped channel of the receiver member to secure the locking device within the receiver member. In a further embodiment, the locking device comprises a top and bottom portion; the bottom portion has a convex recess designed for contacting the curvature of the rod. In still a further embodiment, the screw member, receiver member and the pressure cap may be factory set. The operating physician just needs to attach the screw member to a bone, place the implantation rod into the receiver member and secure the rod into the receiver member using the locking device.
In another embodiment, the present invention relates to a surgical screw and rod implantation system, comprising at least one rod and at least one surgical screw apparatus. The apparatus comprises a screw member having a head and a shaft, the head of the screw member has a spherical undersurface and a conical tapered recess; a receiver member has upper and lower portions, a u-shaped rod receiving channel, and an axial bore; the u-shaped channel has two lateral legs at the upper portion of the receiver member and forms an opening leading to the axial bore; the axial bore near the lower portion of the receiver member includes an inwardly conical tapered surface, the conical tapered surface has a diameter larger than the shaft of the screw member and a diameter smaller than the head of the screw member thereby forming a support upon which the spherical undersurface of the head of the screw member rests when the screw member is guided through the bore to the lower portion of the receiver member; a pressure cap positioned within the axial bore of the receiver member and situated upon the head of the screw member; the pressure cap having upper and lower ends, the upper end of the cap comprising a concave radial portion upon which the rod is positioned, the lower end comprising a spherical portion situated upon the conical tapered recess of the head of the screw member; and a locking device for securing the rod within the u-shaped channel of the receiver member by applying a tightening torque upon the rod when positioned within the opening and the bore near the upper portion of the receiver member.
In still another embodiment, the undersurface of the head and the shaft of the screw member comprise threaded portions. In yet another embodiment, the conical tapered recess of the head of the screw member comprises an aperture coaxial to the shaft and designed to engage a fastening device. The pressure cap further comprises an axial bore extending from the upper through the lower ends of the aperture of the head of the screw member allowing access for the fastening device.
In a further embodiment, the receiver member further comprises a rectangular key-locking segment and a cylindrical undercut situated adjacent to the bore; the pressure cap further comprises a cylindrical undercut and a retaining ring. In still a further embodiment, the key-locking segment and the undercut of the receiver member are designed to engage the undercut and the ring of the cap to form an anti-rotation and locking mechanism.
In yet a further embodiment, the axial bore of the receiver member further comprises a threaded portion and the locking device further comprises a corresponding threaded portion.
In still yet a further embodiment, the axial bore of the receiver member comprises a plurality of slots descending down the legs of the u-shaped channel and the locking device comprising at least one protrusion designed to engage at least one of the slots of the receiver member to secure the locking device within the receiver member. In another further embodiment, the locking device comprises a top and bottom portion; the bottom portion has a convex recess designed for contacting the curvature of the rod.
In another embodiment, the present invention relates to a method of using a surgical screw system with an implantation rod. The method comprises: providing a screw member, a receiver member and a pressure cap; the screw member having a head and a shaft, the head of the screw member having a spherical undersurface and a conical tapered recess; the receiver member has an upper and lower portion, a u-shaped rod receiving channel and an axial bore; the u-shaped rod receiving channel has two lateral legs at the upper portion of the receiver member and forms an opening leading to the axial bore; the axial bore near the lower portion of the receiver member including an inwardly conical tapered surface; the conical surface has a diameter larger than the shaft of the screw member and a diameter smaller than the head of the screw member; the pressure cap has upper and lower ends, the upper end comprising a concave radial portion and the lower end comprising a spherical portion; inserting the screw member into the bore of the receiver member and positioning the screw member toward the lower portion of the receiver member such that the conical surface of the bore forms a support upon which the spherical undersurface of the head of the screw member rests upon the conical surface and the shaft of the screw member extends from the receiver member; inserting the pressure cap into the bore of the receiver member and positioning the spherical portion of the cap upon the conical tapered recess of the head of the screw member, and aligning the concave radial portion of the cap with the u-shaped channel such that the concave radial portion is to ready to receive the rod; securing the screw member into the spinal column of the patient; positioning the rod upon the concave radial portion of the cap; and securing the rod within the u-shaped channel of the receiver member using a locking device; the locking device being positioned within the opening and the bore near the upper portion of the receiver member.
In a further embodiment, the head and the shaft of the screw member comprise threaded portions. In still a further embodiment, the conical tapered recess of the head of the screw member comprises an aperture coaxial to the shaft and designed to engage a fastening device; the cap further comprises an axial bore extending from the upper through lower end of the cap, the bore of the cap corresponding to the aperture of the head of the screw member allowing access for the fastening device.
In still a further embodiment, the screw member is screwed into a spinal column using a fastening device and in another embodiment, the fastening device is a hexagon socket screw key.
In yet a further embodiment, the pressure cap is locked within the bore of the receiver member prior to the screw member being screwed into the spinal column. In still yet a further embodiment, the receiver member further comprises a rectangular key-locking segment and a cylindrical undercut situated adjacent to the bore; the pressure cap furthers comprising a cylindrical undercut and a retaining ring; the key-locking segment and the undercut of the receiver member being designed to engage the undercut and the ring of the cap to form an anti-rotation and locking mechanism.
In another embodiment, the legs of the u-shaped channel of the receiver member further comprise a threaded portion and the locking-device further comprises a corresponding threaded portion. In still another embodiment, the locking device is a set screw and in another embodiment, the locking device is a top locking nut.
In yet another embodiment, the axial bore of the receiver member comprises a plurality of slots descending down the legs of the u-shaped channel and the locking device comprises at least one protrusion designed to engage at least one of the slots of the legs of the u-shaped channel of the receiver member to secure the locking device with the receiver member.
In a further embodiment, the locking device comprises a top and bottom portion; the bottom portion having a convex recess designed for contacting the curvature of the rod. In still a further embodiment, the convex recess of the locking device is aligned with the curvature of the rod before locking the locking device within the receiver member.